1. Field of Invention
The present invention relates to a display device for displaying characters, numbers, patterns, or the like. The present invention also relates to an electronic timepiece, such as a wristwatch or a stopwatch, for giving or measuring time.
2. Description of Related Art
Conventionally, there are widely known display devices which utilize flat displays, such as liquid crystal displays, for displaying numbers, characters, or other information. For example, as shown in FIG. 9, in an electronic timepiece utilizing a liquid crystal display, a pair of polarizers 52 and 53 are placed on both sides of a liquid crystal panel 51, and a light-emitting element 54 is disposed at the back side of the polarizer 53. The pair of polarizers 52 and 53 are disposed such that, for example, their azimuthal angles are set to form a right angle.
During daytime, conventional electronic timepieces display numerical information or the like using external light, whereas during the night they display numerical information or the like using light emitted from the light-emitting element 54, when necessary. Numerical information or the like is displayed by applying a predetermined voltage between the electrodes of the liquid crystal panel 51, with the area to which voltage is not applied appearing as a white background or the like. In the figure, the area to which a voltage is applied to display information is represented as ON, whereas the background color area to which a voltage is not applied is represented as OFF.
As indicated by arrow P, when external light is used to produce background color of a display (liquid crystal panel is turned off), the linearly polarized light component of the external light or natural light, which is oriented parallel to the plane of the figure, passes through the polarizer 52. Then, the polarization direction thereof is twisted 90 degrees by the liquid crystal panel 51 in an off state, causing the linearly polarized light to be oriented perpendicular to the plane of the figure. The linearly polarized light, which has passed through the polarizer 53, is irregularly reflected by a surface of the light-emitting element 54, and part of the irregularly reflected light is transmitted successively back through the polarizer 53, the liquid crystal panel 51, and the polarizer 52 to produce a white background which is perceived by any viewer.
As indicated by arrow Q, when numerical information or the like is to be displayed using external light (the liquid crystal panel 51 is turned on), linearly polarized light, which is oriented parallel to the plane of the figure, is separated from the external light by the polarizer 52, and passes through the liquid crystal panel 51. Since the liquid crystal panel 51 is in an on state, the polarization direction of the linearly polarized light is maintained parallel to the plane of the figure, so that it is absorbed by the polarizer 53. The portion that has absorbed the light appears black to any viewer.
As can be understood from the foregoing description, when external light is used, numbers or the like are displayed on a background having a color corresponding to that reflected from the light-emitting element 54 in order to display the time or other information.
On the other hand, as indicated by arrow C, when a background color is to be produced using light emitted from the light-emitting element 54 (the liquid crystal panel 51 is turned off), the linearly polarized light which is oriented perpendicular to the plane of the figure is separated from randomly polarized light emitted from the light-emitting element 54 by the polarizer 53. Since the liquid crystal panel 51 is in an off state, the polarization direction of the linearly polarized light is twisted 90 degrees by the liquid crystal panel 51, causing the linearly polarized light to be oriented parallel to the plane of the figure. Then, the polarized light passes through the polarizer 52 and is perceived by an outside viewer. The perceived color is the color emitted from the light emitting element 54, which is ordinarily white.
As indicated by arrow D, when numerical information or the like is to be displayed using light emitted from the light emitting element 54 (the liquid crystal panel 51 is turned on), the linearly polarized light, which is oriented perpendicular to the plane of the figure is separated from the light emitted from the light emitting element 54 by the polarizer 53, passes through the liquid crystal panel 51 in an on state, and reaches the polarizer 52. Here, the polarization direction of the linearly polarized light does not match the polarization direction of the polarizer 52, so that the linearly polarized light is absorbed by the polarizer 52. The portion of the polarizer which has absorbed the light, appears black to any viewer.
As can be understood from the foregoing description, when light from the light-emitting element 54 is used, numbers or the like are displayed in black or the like on a background having a color corresponding to the color emitted from the light emitting element 54.
In the above-described conventional electronic timepiece, two polarizers 52 and 53 are disposed on both sides of the liquid crystal panel 51. These polarizers are capable of absorbing linearly polarized light other than that having a predetermined polarization direction. Therefore, the intensity of the light, emitted to the outside for producing a background color or displaying numerical information or the like, may be greatly reduced, causing numerical information or the like to appear dark, and thus difficult to read.
Theoretically speaking, various background colors can be produced, or numerical information or the like can be displayed in various colors by providing a color filter, producing the right color, at a surface of the light-emitting element 54. Actually, however, various display colors cannot be produced, since the light intensity is greatly reduced, so that either a bright, white color or gray had to be used for the display.
In view of the above-described problems, it is an object of the present invention to display numerical information, or the like, and the background, to have a glossy silver metallic tone in order to give a quality appearance to the display.
To achieve the above object, the display devise of the present invention may include a first polarization separator that transmits therethrough linearly polarized light polarized in a first direction and that does not transmit therethrough linearly polarized light polarized in a direction perpendicular to the first direction, a polarization changing element, disposed at a position to receive the linearly polarized light from the first polarization separator, that selects between a state in which a polarization direction of light passing therethrough is changed and a state in which the polarization direction is not changed, and a second polarization separator, diametrically opposed to the first polarization separator with the polarization changing element interposed therebetween, that transmits linearly polarized light polarized in the first direction and reflects linearly polarized light polarized in a direction perpendicular to the first direction, the surface of the second polarization separator facing the polarization changing element being a smooth surface that reflects light in specular reflection.
The electronic watch of the present invention may comprise a first polarization separator that transmits therethrough linearly polarized light polarized in a first direction and that does not transmit therethrough linearly polarized light polarized in a direction perpendicular to the first direction, a polarization changing element, disposed at a position to receive the linearly polarized light from the first polarization separator, for selecting between a state in which a polarization direction of light passing therethrough is changed and a state in which the polarization direction is not changed, a second polarization separator, diametrically opposed to the first polarization separator with the polarization changing element interposed therebetween, that transmits linearly polarized light polarized in a first direction, and that reflects linearly polarized light polarized in a direction perpendicular to the first direction, and a light emitting element arranged on the side of the second-polarization separator opposite to the polarization changing element.
In the above arrangements, the first polarization separator is constructed of an ordinary polarizer. The ordinary polarizer may be a film member which outputs linearly polarized light polarized in one direction in response to an incident natural light, and may be produced by interposing a polarizer layer between protective layers of TAC (cellulose triacetate).
The polarization changing element may be constructed of a liquid crystal element, for example. Liquid crystals may be any of variety of liquid crystals including a TN (Twisted Nematic) liquid crystal, an STN (Super-Twisted Nematic) liquid crystal, and an ECB (Electrically Controlled Birefringence) liquid crystal. The STN liquid crystals employs color compensation, optically anisotropic material, such as an F-STN (Film Compensated Super-Nematic) liquid crystal.
The second polarization separator may be one of (1) the polarization separating film of a multi-layered structure of films as disclosed in International Publication Nos. WO95/17692 and WO95/27919, (2) a polarization separator having a cholesteric liquid crystal with a xcex/4 phase plate on one side or on both sides, (3) a polarization separator that separates a light into a reflected polarized light and a transmitted polarized light taking advantage of the Brewster""s angle (SID 92 DIGEST, pages 427 to 429) and (4) a polarization separator employing the hologram.
The display device and electronic watch of this invention may use the second polarization separator instead of a polarizer arranged behind the polarization changing element in the conventional electronic watch and by the smooth surface of the second polarization separator facing the polarization changing element to reflect light in a specular reflection.
The polarizer generally has the function of transmitting linearly polarized light polarized in a first direction while not transmitting other light by absorption, and in contrast, the second polarization separator transmits linearly polarized light polarized in the first direction while reflecting a light perpendicular to it, particularly, totally reflecting (in specular reflection) the linearly polarized light polarized in a direction perpendicular to the first polarization direction.
With the second polarization separator substituted for the ordinary polarizer, light, which would be conventionally absorbed or dispersed, is reflected contributing to the displaying and brightening the background color and numeric information and the like in the electronic watch. When the second polarization separator is provided with the smooth surface to reflect light in specular reflection without arranging a light scattering layer, namely, a light diffusion layer on the front side (viewing side) of the second polarization separator, the light reflected in specular reflection gives a sufficient amount of light to the viewer without attenuation. When a light scattering layer (light diffusion layer) is arranged on the front side of the second polarization separator, the light specularly reflected by the second polarization separator is scattered, becoming soft but at a sufficient level to the viewer.
The specularly reflected light from the second polarization separator is presented either as the background color or as the color for the numeric information and the like depending on the setting of the polarization direction of the first polarization separator, and in either case, the display device and watch present a glossy, silver-metallic color, high-quality display. In an ordinary electronic watch, the information display area for numeric information and the like is relatively small in area compared to the background color area, and the high-quality display is even more enhanced with the background color presented by the specularly reflected light.
The electronic watch of the present invention may comprise a lamination of a first polarizer which transmits linearly polarized light polarized in a first direction while not transmitting linearly polarized light polarized in a second direction perpendicular to said first direction, a twisted nematic liquid crystal layer which rotates a polarization direction of light transmitted therethrough in an off state while not rotating the polarization direction in an on state, a second polarizer which transmits linearly polarized light polarized in a third direction while reflecting, in specular reflection, linearly polarized light polarized in a fourth direction perpendicular to said third direction, a first optical element, a reflective layer, and a light emitting element laminated in the above order.
With this arrangement, the electronic watch incorporating a bright second polarizer for specular reflection becomes a compact and low power-consumption watch.
In the electronic watch, the reflective layer irregularly reflects light traveling from the second polarizer to the light emitting element. With this arrangement, the irregular reflection on the reflective layer makes the external light opaque white, presenting a bright white background or a bright segment color.
In the electronic watch, the first optical element may be a light absorbing layer. With this arrangement, when the external light is used, the polarized light transmitted through the second polarization separator, out of the external light, is absorbed by the light absorbing layer, and the polarized light transmitted through the second polarization separator is irregularly reflected by the reflective layer, and is further absorbed by the light absorbing layer, light attenuation increases, and light that is again transmitted through the second polarization separator is substantially reduced, thereby keeping a black color. When the light emitting element is used, the light from it is transmitted through the light absorbing layer once, and travels to the second polarization separator, and thereby suffers less attenuation. The emission color itself is seen from the outside.
In the electronic watch, the first optical element may be a coloration layer. With this arrangement, when the external light is used, the polarized light transmitted through the second polarization separator (the second polarizer) is transmitted through the coloration layer, the reflective layer and the coloration layer and then the second polarization separator again and exits externally. For this reason, the color of the polarized light reflected from the second polarization separator (a silver-mirror color when no second optical element is arranged between the TN liquid crystal layer and the second polarization separator, and a white color when a second optical element such as a diffusion layer is arranged between the TN liquid crystal layer and the second polarization separator) contrasts with the color of the polarized light transmitted through the second polarization separator, improving the contrast of the display.
Available as the coloration layer is an orange filter, a green filter or the like, and the color of the polarized light transmitted through the second polarization separator is orange when an orange filter is used, and green when a green filter is used.
In this case, the emission color of the light emitting element is light green when an EL element is used, and is red, green or the like when an LED is used, and a great difference is caused between the emission color (with the light emitting element on) resulting from the light emitting element in the same liquid crystal layer (in on or off) and the color from the external light (the light emitting element off), drawing the viewer""s attention.
In the electronic watch, a second optical element may be arranged between the twisted nematic liquid crystal layer and the second polarizer. In the electronic watch, the second optical element may be either a light diffusion layer or a light scattering layer.
In the electronic watch, a second optical element may be arranged between the twisted nematic liquid crystal layer and the second polarizer.
In these arrangements, when the external light is used, the polarized light may be specularly reflected from the second polarization separator, out of the external light, diffused or scattered, and looks white to the user, and an easy-to-see electronic watch results with a bright and soft color tone but not loud such as silver.
In the electronic watch, the light absorbing layer may be a tracing paper. The light absorbing layer is easily formed using a commercially available tracing paper.
In the electronic watch, the light absorbing layer may have a visible light transmittance within a range from 40% to 80%. More preferably, the light absorbing layer may have a visible light transmittance within a range from 55% to 65%.
With the arrangement in the electronic watch, the external light transmitted through the second polarization separator may be balanced with the emission of the light emitting element transmitted through the second polarization separator, and an easy-to-see electronic watch results.
The electronic watch may have means arranged between the coloration layer and the reflective layer to transmit light from the light emitting element while irregularly reflecting light from the coloration layer. With this arrangement, a copy paper sheet is preferred as the means. Especially when an LED device as the light emitting element is used as a side light, a slant guide plate is used to guide the emission of the LED and to reflect it toward the TN liquid crystal, the light from the LED is made uniform and transmitted, and the light from the coloration layer is irregularly reflected.
In the electronic watch, the light emitting element may comprise an electroluminescence device or a light emitting diode.
The light emitting element may employ a surface emitting type EL element. A compact electronic watch is thus provided. The electronic watch features a low power consumption with the surface emitting LED device or a side light LED device.
By introducing a color difference between the color of the light transmitted through the second polarization separator and the external light reflected from the second polarization separator, the viewer""s attention to the electronic watch is easily called.
Since the color of the segment is the emission color of the light emitting element, a bright display results.
In the electronic watch, a light-transmissive color layer may be arranged between the polarization changing element and the light emitting element. With the color layer arranged between the polarization changing element and the second polarization separator, a glossy metallic color not only of silver but also of other various colors is introduced. Particularly, with a golden layer as the color layer arranged, a golden metallic tone is introduced contributing to a high-quality display.
To form a color layer, a color film of an appropriate color may be glued onto, or a metal powder or other color powder may be sprayed at a density level still assuring a light transmissivity onto, at least one of the surface of the second polarization separator facing the polarization changing element and the surface of the polarization changing element facing the second polarization separator.
In the electronic watch, the light emitting element may comprise an electroluminescence element or a light emitting diode, and may emit light of at least one of orange, red, light green, and green to the twisted nematic liquid crystal layer via the second polarizer.
The electronic watch of the present invention may comprise a lamination of a first polarizer which transmits light polarized in a direction parallel to a first polarization direction while absorbing light polarized in a direction perpendicular to the first polarization direction, a liquid crystal layer which rotates the polarization direction of an incident light by 90 degrees in a non-voltage applied state while not rotating the polarization direction of the incident light in a voltage-applied state, a polarization separator which transmits light polarized in a second polarization direction while reflecting light polarized in a direction perpendicular to the second polarization direction, a first optical element, a reflective element that irregularly reflects light, and a light emitting element that emits an emission color light, laminated in the above order, wherein when the first polarization direction is parallel to the second polarization direction, a first color light from the external light in the non-voltage applied state has the color of the light reflected from the polarization separator while a second color light from the external light in the voltage-applied state has the color of the light transmitted through the first optical element. When the first polarization direction is parallel to the second polarization direction, a third color light from the emission of the light emitting element in the non-voltage applied state is black while a fourth color light from the emission of the light emitting element in the voltage-applied state has the color of the light transmitted through the first optical element. When the first polarization direction is perpendicular to the second polarization direction, a fifth color light from the external light in the non-voltage applied state has the color of the light transmitted through the first optical element while a sixth color light from the external light in the voltage-applied state has the color of the light reflected from the polarization separator. When the first polarization direction is perpendicular to the second polarization direction, a seventh color light from the emission of the light emitting element in the non-voltage applied state has the color of the light transmitted through the first optical element while an eighth color light from the emission of the light emitting element in the voltage applied state is black.
In the electronic watch, a light scattering layer or a light diffusion layer may be arranged between the liquid crystal layer and the polarization separator and both the first color light and the sixth color light are white.
In the electronic watch, the first optical element may be a light absorbing layer, both the second color light and the fifth color light are black, and both the fourth color light and the seventh color light have the emission color.
In the electronic watch, the first optical element may be a coloration layer, both the second color light and the fifth color light are the color attributed to the coloration layer, and both the fourth color light and the seventh color light have the emission color that is colored through the transmission through the coloration layer.
When a coloration layer as the first optical element is provided with a backlight on, the light exiting outwardly is an emitted light colored through the coloration layer. If the EL element is used in this case, the emission color of the EL element is a light color and a resulting color looks like a mixed color of the emission color and the color of the coloration layer because the wavelength characteristics of the EL element is mild. On the other hand, the wavelength characteristics of the LED are sharp, and the emission of the LED is not efficiently transmitted through the coloration layer if it fails to match the coloration layer. The coloration layer for the LED is preferably a band pass filter having wavelength characteristics.
In addition to the aforementioned structural elements:
(1) It is desirable that a light-scattering layer be provided opposite the polarization changing element with the second polarized light separator interposed therebetween, that is at the back side of the second polarization separator with respect to the viewer. With the light-scattering layer provided, when the background color is a glossy metallic color, numerical information or the like can be displayed in a non-glossy color that stands out, whereas when numerical information or the like is displayed in a glossy color, a non-glossy background color can be produced to make the numerical information, or the like, stand out.
(2) In addition to the aforementioned structural elements, a light-emitting element that emits light to the polarization changing element through the second polarization separator may be provided. The light-emitting element which may be used includes: 1) a planar light-emitting element like an electroluminescence (EL) element; 2) a light-emitting device in which a cold cathode, being a linear light source, is disposed at a side end face of a light guide plate having a planar light-emitting surface; and 3) a light emitting device or the like in which a plurality of light emitting diodes (LEDs), being point-like light sources, are disposed in a row at a side end face of a light guide plate having a planar light emitting surface.
When a light-emitting element is used as an additional structural element, the viewer can freely select a display method, that is the display method using external natural light or that using a light-emitting element. In addition, when the second polarization separator, which transmits a linearly polarized light polarized in a certain direction and reflects all other linearly polarized light, is used, instead of an ordinary polarizer, numerical information or the like can be displayed in various forms, and various background colors can be produced, compared to conventional electronic timepieces in which two polarizers are used for displaying information or producing a background color.
For example, in conventional devices, when the display method is switched between that using external natural light and that using the light emitting element, there is not much difference between the background colors and the forms of display of such information as numerical information. For example, when numerical information or the like is displayed in a dark color, such as black, on a background with a color corresponding to the reflected color or the emitted color of the light emitting element, and the display method is switched, only the way in which the background color is produced by the light emitting element is changed, so that the background color is either produced by the reflected color or the emitted color of the light emitting element, ordinarily causing the background color to be the same in both cases. Similarly, when numerical information or the like is displayed in a color corresponding to the reflected color or emitted color of the light emitting element on a background with a dark color, such as black, only the way in which the color of the numerical information or the like is produced by the light emitting element is changed, so that the color of the numerical information or the like is produced either by the reflected color or the emitted color of the light emitting element.
Compared to the above-described conventional devices, the electronic timepiece of the present invention comprising a light emitting element is constructed in such a way as to allow the background color and the form of display of the numerical information or the like to be changed drastically, when the display method switches between that using external natural light and that using the light emitting element. This change may surprise the viewer.
For example, when the display method is switched from that using external natural light to that using the light emitting element, the numerical information or the like displayed in a bright color on a background with a glossy metallic tone that gives quality appearance to the display, is displayed in a bright color produced by the light emitting element on a background having a dark color, such as black. Such a change can surprise the viewer.
(3) It is desirable to construct the light emitting element so that it emits at least one of the following colors: orange, red, or yellowish green. In the electronic timepiece of the present invention, numerical information or the like is displayed in the color emitted by the light emitting element. Since the aforementioned colors stand out against black, when the light emitting element is made to emit any one of the aforementioned colors to display numerical information or the like in any one of these colors, the displayed information becomes bright and easy to read, thereby easily attracting the human eye.
(4) In the foregoing description, nothing was particularly stated about whether the light emitting element is to emit a single color or a plurality of colors. When the light emitting element is constructed to emit a plurality of colors, numerical information or the like can be displayed in several colors in one electronic timepiece, so that displays of a greater variety of colors can be realized.
(5) When the aforementioned light emitting element is used to emit a plurality of colors, the color emitted by the light emitting source itself may be changed, and the light emitting element may be composed of a white light emitting source and a color filter.
(6) As mentioned above, various polarization separating elements can be used for the second polarization separating element, but it is desirable that a polarization separating film, disclosed in International Patent Publication Nos. WO95/17692 or WO95/27919, be used for the second polarization separator.